Stents are generally tubular devices that are used to support a segment of a blood vessel or other anatomical lumen so as to maintain its patency. Stents are useful, for example, in the treatment of atherosclerotic stenoses in blood vessels, maintaining blood perfusion to downstream tissue after opening of a flow restriction (e.g., via balloon angioplasty). Various types of stent designs have been developed for treating diseases of blood vessels and other tubular structures inside the body. The currently available stents can be classified into two broad categories: affirmatively-expandable and self-expanding.
An affirmatively-expandable stent may be collapsed down on a dilatation catheter while in a radially contracted state, for example, a stent may be collapsed down onto a folded balloon on the end of a balloon dilatation catheter. The stent maintains this collapsed configuration until it is expanded by the dilatation catheter. For example, when the stent has been properly positioned within the lumen, the dilatation catheter may be actuated (e.g., by inflating a balloon within the stent to an appropriate size), expanding the stent to the desired diameter. The catheter is then returned to a contracted state (e.g., by balloon deflation), and the catheter is withdrawn, leaving the expanded stent in place within the lumen. The stent typically remains in its expanded state because of the plastic deformation that was imparted to its structural elements during expansion.
An affirmatively-expandable stent has many attractive attributes. For example, its diameter and outward force against the vessel wall can be adjusted, for instance, by controlling the inflation pressure of the balloon. Affirmatively-expandable stents, however, can also present certain disadvantages. For example, one disadvantage of certain stent designs is that there is some degree of elastic recoil after expansion. Such elastic recoil usually means that there is a reduction in diameter after the balloon is deflated. The degree of reduction in diameter is related, for example, to material selection, structural design, and degree of inward force from the vessel wall. Balloon-expandable stents are known that employ ratcheting or latching means for retaining the expanded configuration. For one example of such a stent, see, e.g., Pub. No. U.S. 2004/0093076 to White et al.